1. Field of the Invention
This invention relates generally to internal combustion engines, and more particularly, to means for such an engine which reduces the pollutants discharged into the atmosphere by the engine. More specifically, the invention relates to an apparatus which recirculates or recycles a portion of the exhaust gases from the engine back to the inlet of the carburetor so that the exhaust gases may be burned, thereby reducing the nitrogen oxides discharged into the atmosphere with the exhaust gas from the engine.
2. Prior Art
It is well known that the presence of nitrogen oxide in the exhaust gas from gasoline engines is one of the major causes of air pollution and that the quantity of nitrogen oxide present in the exhaust gas can be reduced by recirculating the exhaust gas through the engine for recombustion.
Accordingly, many efforts have been made in the prior art to design systems for recirculating a portion of the exhaust gas to thereby reduce the emmission of nitrogen oxide into the atmosphere. Examples of some such prior art efforts are exemplified by U.S. Pat. Nos. 3,636,934, 3,807,375, 3,924,589, 3,927,523 and 4,075,992.
It is also known, and all of the aforementioned patents recognize, that in order for the performance of the engine not to be adversely affected, the recirculation of the exhaust gases must be regulated to comply with the mode of operation of the engine. In other words, during certain operations of the engine, as for example cranking, idling, deceleration or high load operation, recirculation of a substantial quantity of exhaust gases would not only adversely affect the performance of the engine and cause fouling of the plugs and combustion chambers thereof, but would also tend to increase pollution of the atmosphere. Alternatively, during acceleration and normal operation of the engine, recirculation of a substantial quantity of the exhaust gases is desired for recombustion of the exhaust gases to thereby reduce the amount of nitrogen oxides present in the exhaust gas.
All of the devices known to applicant, and including those disclosed in the aforementioned patents, comprise apparatus wherein the exhaust gases are recirculated from the exhaust of the engine back to the intake manifold of the engine downstream of the throttle valve in the carburetor. Since the vacuum or pressure condition present in the intake manifold of the engine depends upon both the speed of operation of the engine and the throttle setting of the carburetor, the quantity of exhaust gas recirculated to the intake manifold will thus also depend upon these factors. Therefore, in order to insure that the proper proportion of exhaust gas is recirculated to the intake of the engine during the various modes of operation thereof, separate valve means have been provided in the bypass from the exhaust to the intake manifold to control the flow of the recirculated exhaust gases. Control of these valves has been accomplished by means of thermally responsive devices, pressure responsive devices and direct mechanical linkage devices. Such devices are not only relatively expensive and complicated but are also subject to failure due to the highly corrosive nature of the exhaust gases which are encountered.